1. Field of the Invention
The present invention relates to a method of recovering phosphor from phosphor sludge, especially that emits green upon being excited by electron beams in a picture tube.
2. Description of the Prior Art
Phosphor suspensions for coating frontal glass panels for picture tubes are provided with various additives, especially sodium dichromate, PVA and acrylate. During the coating process any excess suspension will be spun off the glass panel. The suspension spun off will find its way into the so-called phosphor sludge, and the same applied as regards the suspension that, following exposure of the coating, will be washed away from the unexposed parts. Traditionally the phosphor sludge is washed and then collected until a given charge quantity is available. The collected phosphor is dried for one hour at about 200.degree. C. and subsequently calcined at about 400.degree.-450.degree. C. for one hour. This is followed by screening with a relatively coarse mesh size, namely about 60-70 mm, and grinding in a ball mill together with water and PVA. Other customary steps follow especially a prechroming process in a storage tank. This traditional method requires a great deal of time and energy and, given the grinding process, leads to a reduction of the luminosity of the recovered phosphor as compared with the luminosity of virgin phosphor.
Accordingly, there existed the problem of finding a simple method of recovering phosphor for picture tubes from phosphor sludge that would yield recovered phosphor of high quality.